Is Pluto a planet or not? It has moons, so is it a planet?
How do the moons hide? Are the moons hiding behind Pluto?

Haritina Mogosanu, the Publicity Officer for the Royal Astronomical
Society of New Zealand and the Education Coordinator with the
KiwiSpace Foundation, responded.

In 2006 professional astronomers downgraded Pluto to the status
of a 'dwarf planet' after spotting several other similar-sized
objects, using very large telescopes.

These include objects named Haumea, Makemake, and Eris; the
latter seems to be larger than Pluto itself and, like Pluto,
it has a moon. Many moons are bigger than Pluto: our Moon,
Jupiter’s Io, Ganymede, Callisto and Europa, Saturn’s moon
Titan, and Neptune’s Triton.

Having moons is not a condition for a celestial object to
be classified as a planet: for example, Mercury and Venus
have no moons, whereas there are several large asteroids
(orbiting between Mars and Jupiter) which do have moons.
To qualify as being a ‘proper’ planet a body has to be
large enough to be spherical (due to self-gravity), which
Pluto is; and it must dominate its neighbourhood and sweep
it clear of other debris – which is not really what Pluto
does. For example, of the 246 years it takes Pluto to orbit
the Sun, twenty of those years it slips inside Neptune’s orbit.
Besides, Pluto circuits the Sun in a tilted plane that is
quite different from that of the eight major planets
(Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune).
This is another reason to reject it from fully-fledged planet status.

Pluto has at least five moons. You need quite a good telescope
to be able see Pluto itself, and the smaller moons have been
discovered only by using very large ground-based telescopes,
plus the Hubble Space Telescope. As they orbit around Pluto,
each may seem to hide behind it and then emerge again; this
is simply because we are looking at Pluto from Earth. Our
Moon does the same thing – sometimes you can see it at night,
sometimes you can’t – but if you lived in space above the
North or South Pole then you would be able see it all the
time, appearing to go in circles around our own planet.

Don’t feel too sorry for Pluto. It is probably the most
beloved of all the dwarf planets, and definitely a favourite
amongst junior astronomers.